1. Field
The presently disclosed subject matter relates to an optical deflector including meander-type piezoelectric actuators. The optical deflector can be applied to a laser projector, a laser radar, a bar code reader, an area sensor, and other optical apparatus, to reduce their sizes.
2. Description of the Related Art
Generally, in an optical scanner or the like, an optical deflector is constructed by a micro electro mechanical system (MEMS) device manufactured by using semiconductor manufacturing processes and micro machine technology.
A prior art optical deflector as a MEMS device is constructed by a mirror, an outer frame surrounding the mirror, and a pair of meander-type piezoelectric actuators coupled between the mirror and the outer frame and serving as cantilevers for rocking the mirror with respect to a rocking axis of the mirror (see: JP2008-040240A).
In the above-described prior art optical deflector, since the drive force by the meander-type piezoelectric actuators can be increased to increase the flexing angle, the mirror can be driven at a frequency other than the resonant frequency.
In the piezoelectric actuators, two adjacent piezoelectric cantilevers are folded at a rigid folded portion serving as a node. Therefore, when the piezoelectric cantilevers are operated, the piezoelectric cantilevers may be drawn toward the rigid folded portion. As a result, the position of the rocking axis of the mirror is deviated from that of a symmetrical axis such as an X-axis on the plane of the mirror toward the folded portion while the mirror is being rocked, so that an irradiated area cannot accurately be scanned with light reflected from the mirror.
For example, as illustrated in FIG. 1A, the rocking axis of a mirror M coincides with the symmetrical axis (X-axis), so that the mirror M is rocked around the X-axis at a flexing angle α. In this case, when laser light L is incident at an angle of 0° relative to an optical deflector, an imaginary screen S1 is irradiated with reflected lights RL1 and RL2, so that an irradiated area A can be realized on the imaginary screen S1.
On the other hand, as illustrated in FIG. 1B, when the rocking axis of the mirror M is deviated from the X-axis to a position R, the mirror M is rocked around an axis at the position R at a flexing angle 2·α. In this case, when laser light L is incident at an angle of 0° relative to the optical deflector, the imaginary screen S1 is irradiated with reflected lights RL1 and RL2, so that an irradiated area A′ shifted toward the right direction can be realized on the imaginary screen S1. Thus, an image generated on the imaginary screen S1 may be shifted to the right direction.
Also, as illustrated in FIG. 2A, the rocking axis of the mirror M coincides with the X-axis, so that the mirror M is rocked around the X-axis at a flexing angle α. In this case, when laser light L is incident at an angle of −45° relative to the optical deflector, an imaginary screen S2 is irradiated with reflected lights RL1 and RL2, so that an irradiated area A can be realized on the imaginary screen S2.
On the other hand, as illustrated in FIG. 2B, when the rocking axis of the mirror M is deviated from the X-axis to a position R, the mirror M is rocked around an axis at the position R at a flexing angle 2·α. In this case, when laser light L is incident at an angle of −45° relative to the optical deflector, the imaginary screen S2 is irradiated with reflected lights RL1 and RL2, so that an enlarged irradiated area A′ can be realized on the imaginary screen S2. Thus, an image generated on the imaginary screen S2 may be enlarged.
Further, as illustrated in FIG. 3A, the rocking axis of the mirror M coincides with the X-axis, so that the mirror M is rocked around the X-axis at a flexing angle α. In this case, when laser light L is incident at an angle of +45° relative to the optical deflector, an imaginary screen S3 is irradiated with reflected lights RL1 and RL2, so that an irradiated area A can be realized on the imaginary screen S3.
On the other hand, as illustrated in FIG. 3B, when the rocking axis of the mirror M is deviated from the X-axis to a position R, the mirror M is rocked around an axis at the position R at a flexing angle 2·α. In this case, when laser light L is incident at an angle of +45° relative to the optical deflector, the imaginary screen S3 is irradiated with reflected lights RL1 and RL2, so that a reduced irradiated area A′ can be realized on the imaginary screen S3. Thus, a reduced image generated on the imaginary screen S3 may be obtained.
In view of the foregoing, it is required to suppress the deviation of the rocking axis of the mirror from a symmetrical axis (X-axis) on the mirror toward a folded portion of the piezoelectric cantilevers.